Advanced semiconductor submicron technologies require multilevel metallization (MLM) schemes which reduce interconnection lengths to provide lower RC time delays and enhanced performance. MLM schemes also permit increased device densification, due to the ability to use the third (vertical) dimension, and easier signal routing because of higher flexibility in architectural design. However, these schemes necessitate new interconnect metals to handle the higher current densities resulting from decreasing the dimensions of device features without loss of electrical and structural integrities, and to deliver the sheet resistance required to meet performance demands. They also require new deposition techniques to satisfactorily grow these newer interconnect metals and metal films and to successfully produce the increasingly complex architectures as lateral feature sizes are scaled down more rapidly than conductor or insulator thicknesses.
One of the most suitable metal deposition processes, in terms of providing the reliability and reproducibility in forming the multilevel structures of metals and dielectrics required, is chemical vapor deposition (CVD). CVD involves transporting volatile metal-organic precursors, which contain the elemental constituents of the target material, into a reactor. The deposition on a substrate in the reactor occurs through: (a) reactions in the gas phase leading to species which condense on the substrate to form the desired film and film pattern and/or (b) reactions of adsorbed species on the substrate surface which catalyzes or aids the decomposition into the desired film and gaseous byproducts which are continuously pumped out. One of the key advantages of CVD is its potential ability to involve the substrate surface in the deposition reaction which would lead, under the proper conditions, to a conformal, planarized blanket, or selective (patterned) metal growth. This feature is an important requirement to produce three-dimensional multilevel structures which contain interconnections in the vertical direction through vias and holes in the dielectric or substrate.
Another important characteristic of CVD is that it can produce materials on substrates of complex shape and form at growth rates which are much higher than the minimum acceptable in the electronic device industry. In addition, it can grow materials at reduced temperatures, as low as 100.degree. C., with no need for post-deposition annealing. This is necessary to minimize the effects of interdiffusion and to allow the growth of abrupt multilayered structures. It is relatively simple and controllable, and leads to good adherence, high uniformity over a large area, and reduced susceptibility to interfacial mixing and cross-contamination effects. These unique features have made CVD the technique of choice for semiconductor applications, as documented by the extensive research and development (R&D) efforts presently underway to produce manufacturable blanket and selective CVD processes for the growth of metals, metallic alloys, and dielectrics for incorporation in MLM schemes.
These R&D efforts have already produced substantial progress in tungsten (W) CVD metallization and have led to the incorporation of W CVD, which employs the gaseous precursor tungsten hexafluoride (WF.sub.6), in selected manufacturing processes used, for example, in fabrication of the 64 Mb chip. Aluminum and copper CVD metallizations have also witnessed some degree of success, with triisobutylaluminum (TIBA) and trimethylamine-alane (TMAA1), and copper (I) and copper (II) chemistries being successfully employed to grow highly pure and dense aluminum and copper films. In spite of these advances, however, the incorporation of many CVD processes in technologically useful processes has been limited by the lack of a suitable solid precursor delivery technique which exhibits the required levels of reproducibility and control typically associated with liquid and gas precursor delivery systems.
As a result, the delivery of solid precursors in CVD processing is carried out using the sublimator/bubbler method in which the precursor is usually placed in a sublimator/bubbler reservoir which is then heated to the sublimation temperature of the precursor to transform it into a gaseous compound which is transported into the CVD reactor with a carrier gas such as hydrogen, argon, or nitrogen. The introduction of the carrier gas into the sublimator is controlled by a valve, while the flow of (precursor+carrier gas) into the CVD reactor is controlled with a hot-source mass flow controller (MFC), which is heated to a temperature that prevents the precursor from recondensing inside it. However, this design suffers from numerous problems which include undesirable heat-induced effects such as premature decomposition of the precursor and changes in the characteristics of the precursor (such as reduction in volatility with time), limited flow ranges because of physical constraints on pressure drops through the MFC, and lack of accurate flow control because of the unavailability of critical precursor parameters such as heat capacity and compressibility.
Efforts to alleviate these problems through the development of improved solid source delivery systems have encountered limited success and have involved complex equipment and procedures, providing a continuing need for an improved method of delivering solid precursors for use in film deposition procedures such as the chemical vapor deposition of advanced electronic, optoelectronic, photonic, and ceramic materials for various technological applications, including metals, metallic alloys, and dielectrics for semiconductor chip metallization. Such technical applications are hereinafter referred to as "advanced technology" or "advanced technologies."